Method of operating semiconductor memory device with floating body transistor using silicon controlled rectifier principle

ABSTRACT

Methods of operating semiconductor memory devices with floating body transistors, using a silicon controlled rectifier principle are provided, as are semiconductor memory devices for performing such operations. A method of maintaining the data state of a semiconductor dynamic random access memory cell is provided, wherein the memory cell comprises a substrate being made of a material having a first conductivity type selected from p-type conductivity type and n-type conductivity type; a first region having a second conductivity type selected from the p-type and n-type conductivity types, the second conductivity type being different from the first conductivity type; a second region having the second conductivity type, the second region being spaced apart from the first region; a buried layer in the substrate below the first and second regions, spaced apart from the first and second regions and having the second conductivity type; a body region formed between the first and second regions and the buried layer, the body region having the first conductivity type; and a gate positioned between the first and second regions and adjacent the body region. The memory cell is configured to store a first data state which corresponds to a first charge in the body region in a first configuration, and a second data state which corresponds to a second charge in the body region in a second configuration. The method includes: providing the memory cell storing one of the first and second data states; and applying a positive voltage to a substrate terminal connected to the substrate beneath the buried layer, wherein when the body region is in the first state, the body region turns on a silicon controlled rectifier device of the cell and current flows through the device to maintain configuration of the memory cell in the first memory state, and wherein when the memory cell is in the second state, the body region does not turn on the silicon controlled rectifier device, current does not flow, and a blocking operation results, causing the body to maintain the second memory state.

This application is a continuation application of co-pending applicationSer. No. 14/956,103, filed Dec. 1, 2015, which is a continuationapplication of application Ser. No. 14/444,109, filed Jul. 28, 2014, nowU.S. Pat. No. 9,230,965, which issued on Jan. 5, 2016, which is acontinuation application of application Ser. No. 14/023,246, filed Sep.10, 2013, now U.S. Pat. No. 8,837,247, which issued on Sep. 16, 2014,which is a continuation application of application Ser. No. 13/244,916,filed Sep. 26, 2011, now U.S. Pat. No. 8,559,257 which issued on Oct.15, 2013, which is a continuation application of application Ser. No.12/533,661, filed Jul. 31, 2009, now U.S. Pat. No. 8,077,536, whichissued on Dec. 13, 2011, and which claims the benefit of U.S.Provisional Application No. 61/086,170, filed Aug. 5, 2008, whichapplications and patents are each hereby incorporated herein, in theirentireties, by reference thereto. We claim priority to application Ser.Nos. 14/956,103; 14/444,109; 14/023,246; 13/244,916 and 12/533,661 under35 U.S.C. Section 120 and claim priority to Application Ser. No.61/086,170 under 35 U.S.C. Section 119.

FIELD OF THE INVENTION

The present invention relates to semiconductor memory technology. Morespecifically, the present invention relates to dynamic random accessmemory having an electrically floating body transistor.

BACKGROUND OF THE INVENTION

Semiconductor memory devices are used extensively to store data. DynamicRandom Access Memory (DRAM) is widely used in many applications.Conventional DRAM cells consist of a one-transistor and one-capacitor(1T/1C) structure. As the 1T/1C memory cell feature is being scaled,difficulties arise due to the necessity of maintaining the capacitancevalues of each memory scale in the scaled architecture.

There is a need in the art for improve DRAM memory that can betterretain capacitance values in the cells of a scaled architecturecomprising many DRAM memory cells. Because of the rapid growth in theamounts of memory used by modern electronic devices, there is acontinuing need to provided improvement in DRAM architecture that allowfor a smaller cell size than the currently available 1T./1C memory cellarchitecture.

Currently existing DRAM memory must be periodically refreshed tomaintain the viability of the data stored therein, as the stored chargeshave a finite lifetime and begin to degrade after a period of time. Thecharges therefore need to be refreshed to their originally storedvalues. To do this, the data is first read out and then it is writtenback into the DRAM. This process must be repeated cyclically after eachpassage of a predetermined period of time, and is inefficient, as it isboth time consuming and energy inefficient.

Thus, there is a need for DRAM memory that is both space efficient andcan be efficiently refreshed.

The present inventions satisfies these needs as well as providingadditional features that will become apparent upon reading thespecification below with reference to the figures.

SUMMARY OF THE INVENTION

The present invention provides methods of operating semiconductor memorydevices with floating body transistors, using a silicon controlledrectifier principle and also provide semiconductor memory devices forsuch operations.

A method of maintaining the data state of a semiconductor dynamic randomaccess memory cell is provided, wherein the memory cell comprises asubstrate being made of a material having a first conductivity typeselected from p-type conductivity type and n-type conductivity type; afirst region having a second conductivity type selected from the p-typeand n-type conductivity types, the second conductivity type beingdifferent from the first conductivity type; a second region having thesecond conductivity type, the second region being spaced apart from thefirst region; a buried layer in the substrate below the first and secondregions, spaced apart from the first and second regions and having thesecond conductivity type; a body region formed between the first andsecond regions and the buried layer, the body region having the firstconductivity type; and a gate positioned between the first and secondregions and adjacent the body region. The memory cell is configured tostore a first data state which corresponds to a first charge in the bodyregion in a first configuration, and a second data state whichcorresponds to a second charge in the body region in a secondconfiguration. The method includes: providing the memory cell storingone of the first and second data states; and applying a positive voltageto a substrate terminal connected to the substrate beneath the buriedlayer, wherein when the body region is in the first state, the bodyregion turns on a silicon controlled rectifier device of the cell andcurrent flows through the device to maintain configuration of the memorycell in the first memory state, and wherein when the memory cell is inthe second state, the body region does not turn on the siliconcontrolled rectifier device, current does not flow, and a blockingoperation results, causing the body to maintain the second memory state.

In at least one embodiment, the memory cell includes, in addition to thesubstrate terminal, a source line terminal electrically connected to oneof the first and second regions; a bit line terminal electricallyconnected to the other of the first and second regions; a word lineterminal connected to the gate; and a buried well terminal electricallyconnected to the buried layer; the method further comprising: applying asubstantially neutral voltage to the bit line terminal; applying anegative voltage to the word line terminal; and allowing the source lineterminal and the buried well terminal to float.

In at least one embodiment, the memory cell includes, in addition to thesubstrate terminal, a source line terminal electrically connected to oneof the first and second regions; a bit line terminal electricallyconnected to the other of the first and second regions; a word lineterminal connected to the gate; and a buried well terminal electricallyconnected to the buried layer; the method further comprising: applying asubstantially neutral voltage to the source line terminal; applying anegative voltage to the word line terminal; and allowing the bit lineterminal and the buried well terminal to float.

A method of reading the data state of a semiconductor dynamic randomaccess memory cell is provided, wherein the memory cell comprises asubstrate being made of a material having a first conductivity typeselected from p-type conductivity type and n-type conductivity type; afirst region having a second conductivity type selected from the p-typeand n-type conductivity types, the second conductivity type beingdifferent from the first conductivity type; a second region having thesecond conductivity type, the second region being spaced apart from thefirst region; a buried layer in the substrate below the first and secondregions, spaced apart from the first and second regions and having thesecond conductivity type; a body region formed between the first andsecond regions and the buried layer, the body region having the firstconductivity type; and a gate positioned between the first and secondregions and adjacent the body region. The memory cell further comprisesa substrate terminal electrically connected to the substrate, a sourceline terminal electrically connected to one of the first and secondregions, a bit line terminal electrically connected to the other of thefirst and second regions, a word line terminal connected to the gate,and a buried well terminal electrically connected to the buried layer;wherein each memory cell is configured to store a first data state whichcorresponds to a first charge in the body region in a firstconfiguration, and a second data state which corresponds to a secondcharge in the body region in a second configuration. The methodincludes: applying a positive voltage to the substrate terminal;applying a positive voltage to the word line terminal; applying asubstantially neutral voltage to the bit line terminal; and allowingvoltage levels of the source line terminal and the buried well terminalto float; wherein, when the memory cell is in the first data state, asilicon controlled rectifier device is formed by the substrate, buriedwell, body region and region connected to the bit line terminal is inlow-impedance, conducting mode, and a higher cell current is observed atthe bit line terminal compared to when the memory cell is in the seconddata state, as when the memory cell is in the second data state, thesilicon rectifier device is in blocking mode.

A semiconductor memory array is provided, including: a plurality ofsemiconductor dynamic random access memory cells arranged in a matrix ofrows and columns, each semiconductor dynamic random access memory cellincluding: a substrate having a top surface, the substrate being made ofa material having a first conductivity type selected from p-typeconductivity type and n-type conductivity type; a first region having asecond conductivity type selected from the p-type and n-typeconductivity types, the second conductivity type being different fromthe first conductivity type, the first region being formed in thesubstrate and exposed at the top surface; a second region having thesecond conductivity type, the second region being formed in thesubstrate, spaced apart from the first region and exposed at the topsurface; a buried layer in the substrate below the first and secondregions, spaced apart from the first and second regions and having thesecond conductivity type; a body region formed between the first andsecond regions and the buried layer, the body region having the firstconductivity type; and a gate positioned between the first and secondregions and above the top surface; a source line terminal electricallyconnected to one of the first and second regions; a bit line terminalelectrically connected to the other of the first and second regions; aword line terminal connected to the gate; a buried well terminalelectrically connected to the buried layer; and a substrate terminalelectrically connected to the substrate below the buried layer; whereineach memory cell further includes a first data state which correspondsto a first charge in the body region, and a second data state whichcorresponds to a second charge in the body region; wherein each of theterminals is controlled to perform operations on each the cell; andwherein the terminals are controlled to perform a refresh operation by anon-algorithmic process.

In at least one embodiment, the data state of at least one of the cellsis read by: applying a neutral voltage state to the substrate terminal,applying a voltage greater than or equal to zero to the buried wellterminal, applying a neutral voltage to the source line terminal,applying a positive voltage to the bit line terminal and applying apositive voltage to the word line terminal.

In at least one embodiment, the data state of at least one of the cellsis read by: applying a positive voltage to the substrate terminal,applying a neutral voltage to the bit line terminal, applying a positivevoltage to the word line terminal and leaving the source line terminaland the buried well terminal floating.

In at least one embodiment, the first data state is written to at leastone of the cells by: applying a positive voltage to the bit lineterminal, applying a neutral voltage to the source line terminal,applying a negative voltage to the word line terminal, applying apositive voltage to the buried well terminal and applying a neutralvoltage to the substrate terminal.

In at least one embodiment, the first data state is written to at leastone of the cells by: applying a positive voltage to the substrateterminal, applying a neutral voltage to the source line terminal,applying a positive voltage to the bit line terminal, applying apositive voltage to the word line terminal and allowing the buried wellterminal to float.

In at least one embodiment, the first data state is written to at leastone of the cells by: applying a neutral voltage to the bit lineterminal, applying a positive voltage to the word line terminal,applying a positive voltage to the substrate terminal and allowing thesource line terminal and the buried well terminal to float.

In at least one embodiment, the second data state is written to at leastone of the cells by: applying a negative voltage to the source lineterminal, applying a voltage less than or equal to about zero to theword line terminal, applying a neutral voltage to the substrateterminal, applying a voltage greater than or equal to zero to the buriedwell terminal, and applying a neutral voltage to the bit line terminal.

In at least one embodiment, the second data state is written to at leastone of the cells by: applying a positive voltage to the bit lineterminal, applying a positive voltage to the word line terminal,applying a positive voltage to the substrate terminal, while allowingthe source line terminal and the buried well terminal to float.

In at least one embodiment, a holding operation is performed on at leastone of the cells by: applying a substantially neutral voltage to the bitline terminal, applying a neutral or negative voltage to the word lineterminal, and applying a positive voltage to the substrate terminal,while allowing the source line terminal and the buried well terminal tofloat.

A semiconductor memory array is provided, including: a plurality ofsemiconductor dynamic random access memory cells arranged in a matrix ofrows and columns, each semiconductor dynamic random access memory cellincluding: a substrate being made of a material having a firstconductivity type selected from p-type conductivity type and n-typeconductivity type; a first region having a second conductivity typeselected from the p-type and n-type conductivity types, the secondconductivity type being different from the first conductivity type; asecond region having the second conductivity type, the second regionbeing spaced apart from the first region; a buried layer in thesubstrate below the first and second regions, spaced apart from thefirst and second regions and having the second conductivity type; a bodyregion formed between the first and second regions and the buried layer,the body region having the first conductivity type; and a gatepositioned between the first and second regions and adjacent the bodyregion; wherein each memory cell further includes a first data statewhich corresponds to a first charge in the body region, and a seconddata state which corresponds to a second charge in the body region;wherein the substrates of a plurality of the cells are connected to asame substrate terminal; and wherein data states of the plurality ofcells are maintained by biasing the substrate terminal.

In at least one embodiment, the cells are refreshed by a non-algorithmicprocess.

In at least one embodiment, the voltage applied to the substrateterminal automatically activates each cell of the plurality of cellsthat has the first data state to refresh the first data state, andwherein each cell of the plurality of cells that has the second datastate automatically remains deactivated upon application of the voltageto the substrate terminal so that each the cell having the second datastate remains in the second data state.

In at least one embodiment, the substrate terminal is periodicallybiased by pulsing the substrate terminal and wherein the data states ofthe plurality of cells are refreshed upon each the pulse.

In at least one embodiment, the substrate terminal is constantly biasedand the plurality of cells constantly maintain the data states.

In at least one embodiment, the substrate has a top surface, the firstregion is formed in the substrate and exposed at the top surface;wherein the second region is formed in the substrate and exposed at thetop surface; and wherein the gate is positioned above the top surface.

In at least one embodiment, the first and second regions are formed in afin that extends above the buried layer, the gate is provided onopposite sides of the fin, between the first and second regions, and thebody region is between the first and second regions and between the gateon opposite sides of the fin.

In at least one embodiment, the gate is additionally provided adjacent atop surface of the body region.

These and other features of the invention will become apparent to thosepersons skilled in the art upon reading the details of the devices andmethods as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, schematic view of a memory cell accordingto an embodiment of the present invention.

FIGS. 2A-2B illustrate various voltage states applied to terminals of amemory cell or plurality of memory cells, to carry out various functionsaccording to various embodiments of the present invention.

FIG. 3 illustrates an operating condition for a write state “1”operation that can be carried out on a memory cell according to anembodiment of the present invention.

FIG. 4 illustrates an operating condition for a write state “0”operation that can be carried out on a memory cell according to anembodiment of the present invention.

FIG. 5 illustrates a holding operation that can be carried out on amemory cell according to an embodiment of the present invention.

FIGS. 6-7 illustrate cross-sectional schematic illustrations of fin-typesemiconductor memory cell devices according to embodiments of thepresent invention

FIG. 8 illustrate a top view of a fin-type semiconductor memory celldevice according to the embodiment shown in FIG. 6.

FIG. 9 is a schematic diagram showing an example of array architectureof a plurality memory cells according to an embodiment of the presentinvention.

FIG. 10 is a schematic diagram showing an example of array architectureof a plurality memory cells according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present devices and methods are described, it is to beunderstood that this invention is not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present invention will be limited only by the appendedclaims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned herein areincorporated herein by reference to disclose and describe the methodsand/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “amemory cell” includes a plurality of such memory cells and reference to“the device” includes reference to one or more devices and equivalentsthereof known to those skilled in the art, and so forth.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Definitions

When a terminal is referred to as being “left floating”, this means thatthe terminal is not held to any specific voltage, but is allowed tofloat to a voltage as driven by other electrical forces with the circuitthat it forms a part of.

The term “refresh” or “refresh operation” refers to a process ofmaintaining charge (and the corresponding data) of a memory cell,typically a dynamic random access memory (DRAM) cell. Periodic refreshoperations of a DRAM cell are required because the stored charge leaksout over time.

Description

The present invention provides capacitorless DRAM memory cells that arerefreshable by a non-algorithmic process. Alternatively, the memorycells may be operated to maintain memory states without the need torefresh the memory states, similar to SRAM memory cells.

FIG. 1 shows an embodiment of a memory cell 50 according to the presentinvention. The cell 50 includes a substrate 12 of a first conductivitytype, such as a p-type conductivity type, for example. Substrate 12 istypically made of silicon, but may comprise germanium, silicongermanium, gallium arsenide, carbon nanotubes, or other semiconductormaterials known in the art. The substrate 12 has a surface 14. A firstregion 16 having a second conductivity type, such as n-type, forexample, is provided in substrate 12 and is exposed at surface 14. Asecond region 18 having the second conductivity type is also provided insubstrate 12, and is also exposed at surface 14. Second region 18 isspaced apart from the first region 16, as shown. First and secondregions 16 and 18 are formed by an implantation process formed on thematerial making up substrate 12, according to any of implantationprocesses known and typically used in the art.

A buried layer 22 of the second conductivity type is also provided inthe substrate 12, buried in the substrate 12, as shown. Buried layer 22is also formed by an ion implantation process on the material ofsubstrate 12. A body region 24 of the substrate 12 is bounded by surface14, first and second regions 16,18, insulating layers 26 and buriedlayer 22. Insulating layers 26 (e.g., shallow trench isolation (STI)),may be made of silicon oxide, for example. Insulating layers 26 insulatecell 50 from neighboring cells 50 when multiple cells 50 are joined inan array 80 to make a memory device. A gate 60 is positioned in betweenthe regions 16 and 18, and above the surface 14. The gate 60 isinsulated from surface 14 by an insulating layer 62. Insulating layer 62may be made of silicon oxide and/or other dielectric materials,including high-K dielectric materials, such as, but not limited to,tantalum peroxide, titanium oxide, zirconium oxide, hafnium oxide,and/or aluminum oxide. The gate 60 may be made of polysilicon materialor metal gate electrode, such as tungsten, tantalum, titanium and theirnitrides.

Cell 50 further includes word line (WL) terminal 70 electricallyconnected to gate 60, source line (SL) terminal 72 electricallyconnected to one of regions 16 and 18 (connected to 16 as shown, butcould, alternatively, be connected to 18), bit line (BL) terminal 74electrically connected to the other of regions 16 and 18, buried well(BW) terminal 76 electrically connected to buried layer 22, andsubstrate terminal 78 electrically connected to substrate 12 at alocation beneath buried layer 22.

FIG. 2 illustrates relative voltages that can be applied to theterminals of memory cell 50 to perform various operations. For a readoperation, a neutral voltage (i.e., about zero volts) is applied to thesubstrate terminal 78, a neutral or positive voltage (greater than orequal to about zero volts) is applied to the BW terminal 76, a neutralvoltage (about zero volts) is applied to SL terminal 72, a positivevoltage is applied to BL terminal 74, and a positive voltage is appliedto WL terminal 70, with the voltage at terminal 70 being more positive(higher voltage) that the voltage applied to terminal 74. If cell 50 isin a state “1” having holes in the body region 24, then a lowerthreshold voltage (gate voltage where the transistor is turned on) isobserved compared to the threshold voltage observed when cell 50 is in astate “0” having no holes in body region 24. In one particularnon-limiting embodiment, about 0.0 volts is applied to terminal 72,about +0.4 volts is applied to terminal 74, about +1.2 volts is appliedto terminal 70, about +0.6 volts is applied to terminal 76, and about0.0 volts is applied to terminal 78. However, these voltage levels mayvary.

Alternatively, a neutral voltage is applied to the substrate terminal78, a neutral or positive voltage is applied to the BW terminal 76, aneutral voltage is applied to SL terminal 72, a positive voltage isapplied to BL terminal 74, and a positive voltage is applied to WLterminal 70, with the voltage at terminal 74 being more positive (highervoltage) that the voltage applied to terminal 70. If cell 50 is in astate “1” having holes in the body region 24, then the parasitic bipolartransistor formed by the SL terminal 72, floating body 24, and BLterminal 74 will be turned on and a higher cell current is observedcompared to when cell 50 is in a state “0” having no holes in bodyregion 24. In one particular non-limiting embodiment, about 0.0 volts isapplied to terminal 72, about +3.0 volts is applied to terminal 74,about +0.5 volts is applied to terminal 70, about +0.6 volts is appliedto terminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary.

Alternatively, a positive voltage is applied to the substrate terminal78, a substantially neutral voltage is applied to BL terminal 74, and apositive voltage is applied to WL terminal 70. The SL terminal 72 andthe BW terminal 76 are left floating, as shown in FIG. 2. Cell 50provides a P1-N2-P3-N4 silicon controlled rectifier device, withsubstrate 78 functioning as the P1 region, buried layer 22 functioningas the N2 region, body region 24 functioning as the P3 region and region16 or 18 functioning as the N4 region. In this example, the substrateterminal 78 functions as the anode and terminal 72 or terminal 74functions as the cathode, while body region 24 functions as a p-base toturn on the SCR device. If cell 50 is in a state “1” having holes in thebody region 24, the silicon controlled rectifier (SCR) device formed bythe substrate, buried well, floating body, and the BL junction will beturned on and a higher cell current is observed compared to when cell 50is in a state “0” having no holes in body region 24. A positive voltageis applied to WL terminal 70 to select a row in the memory cell array 80(e.g., see FIGS. 9-10), while negative voltage is applied to WL terminal70 for any unselected rows. The negative voltage applied reduces thepotential of floating body 24 through capacitive coupling in theunselected rows and turns off the SCR device of each cell 50 in eachunselected row. In one particular non-limiting embodiment, about +0.8volts is applied to terminal 78, about +0.5 volts is applied to terminal70 (for the selected row), and about 0.0 volts is applied to terminal74. However, these voltage levels may vary.

FIG. 3 illustrate a write state “1” operation that can be carried out oncell 50 according to an embodiment of the invention, by performingband-to-band tunneling hot hole injection or impact ionization hot holeinjection. To write state “1” using band-to-band tunneling mechanism,the following voltages are applied to the terminals: a positive voltageis applied to BL terminal 74, a neutral voltage is applied to SLterminal 72, a negative voltage is applied to WL terminal 70, a positivevoltage is applied to BW terminal 76, and a neutral voltage is appliedto the substrate terminal 78. Under these conditions, holes are injectedfrom BL terminal 74 into the floating body region 24, leaving the bodyregion 24 positively charged. In one particular non-limiting embodiment,a charge of about 0.0 volts is applied to terminal 72, a voltage ofabout +2.0 volts is applied to terminal 74, a voltage of about −1.2volts is applied to terminal 70, a voltage of about +0.6 volts isapplied to terminal 76, and about 0.0 volts is applied to terminal 78.However, these voltage levels may vary.

Alternatively, to write state “1” using impact ionization mechanism, thefollowing voltages are applied to the terminals: a positive voltage isapplied to BL terminal 74, a neutral voltage is applied to SL terminal72, a positive voltage is applied to WL terminal 70, a positive voltageless than the positive voltage applied to BL terminal 74 is applied toBW terminal 76, and a neutral voltage is applied to the substrateterminal 78. Under these conditions, holes are injected from BL terminal74 into the floating body region 24, leaving the body region 24positively charged. In one particular non-limiting embodiment, +0.0volts is applied to terminal 72, a voltage of about +2.0 volts isapplied to terminal 74, a charge of about +0.5 volts is applied toterminal 70, a charge of about +0.6 volts is applied to terminal 76, andabout 0.0 volts is applied to terminal 78. However, these voltage levelsmay vary.

In an alternate write state “1” using impact ionization mechanism, apositive bias can be applied to substrate terminal 78, a positivevoltage greater than or equal to the positive voltage applied tosubstrate terminal 78 is applied to BL terminal 74, a neutral voltage isapplied to SL terminal 72, a positive voltage is applied to WL terminal70, while the BW terminal 76 is left floating. The parasitic siliconcontrolled rectifier device of the selected cell is now turned off dueto the negative potential between the substrate terminal 78 and the BLterminal 74. Under these conditions, electrons will flow near thesurface of the transistor, and generate holes through the impactionization mechanism. The holes are subsequently injected into thefloating body region 24. In one particular non-limiting embodiment,about +0.0 volts is applied to terminal 72, a voltage of about +2.0volts is applied to terminal 74, a voltage of about +0.5 volts isapplied to terminal 70, and about +0.8 volts is applied to terminal 78,while terminal 76 is left floating. However, these voltage levels mayvary, while maintaining the relative relationships between the chargesapplied, as described above.

Alternatively, the silicon controlled rectifier device of cell 50 can beput into a state “1” (i.e., by performing a write “1” operation) byapplying the following bias: a neutral voltage is applied to BL terminal74, a positive voltage is applied to WL terminal 70, and a positivevoltage is applied to the substrate terminal 78, while SL terminal 72and BW terminal 76 are left floating. The positive voltage applied tothe WL terminal 70 will increase the potential of the floating body 24through capacitive coupling and create a feedback process that turns theSCR device on. Once the SCR device of cell 50 is in conducting mode(i.e., has been “turned on”) the SCR becomes “latched on” and thevoltage applied to WL terminal 70 can be removed without affecting the“on” state of the SCR device. In one particular non-limiting embodiment,a voltage of about 0.0 volts is applied to terminal 74, a voltage ofabout +0.5 volts is applied to terminal 70, and about +3.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the voltages applied, asdescribed above, e.g., the voltage applied to terminal 78 remainsgreater than the voltage applied to terminal 74.

A write “0” operation of the cell 50 is now described with reference toFIG. 2B and FIG. 4. To write “0” to cell 50, a negative bias is appliedto SL terminal 72, a neutral voltage is applied to BL terminal 74, aneutral or negative voltage is applied to WL terminal 70, a neutral orpositive voltage is applied to BW terminal 76 and a neutral voltage isapplied to substrate terminal 78. Under these conditions, the p-njunction (junction between 24 and 18) is forward-biased, evacuating anyholes from the floating body 24. In one particular non-limitingembodiment, about −2.0 volts is applied to terminal 72, about −1.2 voltsis applied to terminal 70, about 0.0 volts is applied to terminal 74,about +0.6 volts is applied to terminal 76 and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. Alternatively, the voltages applied to terminals 72 and74 may be switched.

Alternatively, a write “0” operation can be performed by putting thesilicon controlled rectifier device into the blocking mode. This can beperformed by applying the following bias: a positive voltage is appliedto BL terminal 74, a positive voltage is applied to WL terminal 70, anda positive voltage is applied to the substrate terminal 78, whileleaving SL terminal 72 and BW terminal 76 floating. Under theseconditions the voltage difference between anode and cathode, defined bythe voltages at substrate terminal 78 and BL terminal 74, will becometoo small to maintain the SCR device in conducting mode. As a result,the SCR device of cell 50 will be turned off. In one particularnon-limiting embodiment, a voltage of about +0.8 volts is applied toterminal 74, a voltage of about +0.5 volts is applied to terminal 70,and about +0.8 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

A holding or standby operation is described with reference to FIGS. 2Band 5. Such holding or standby operation is implemented to enhance thedata retention characteristics of the memory cells 50. The holdingoperation can be performed by applying the following bias: asubstantially neutral voltage is applied to BL terminal 74, a neutral ornegative voltage is applied to WL terminal 70, and a positive voltage isapplied to the substrate terminal 78, while leaving SL terminal 72 andBW terminal 76 floating. Under these conditions, if memory cell 50 is inmemory/data state “1” with positive voltage in floating body 24, the SCRdevice of memory cell 50 is turned on, thereby maintaining the state “1”data. Memory cells in state “0” will remain in blocking mode, since thevoltage in floating body 24 is not substantially positive and thereforefloating body 24 does not turn on the SCR device. Accordingly, currentdoes not flow through the SCR device and these cells maintain the state“0” data. In this way, an array of memory cells 50 can be refreshed byperiodically applying a positive voltage pulse through substrateterminal 78. Those memory cells 50 that are commonly connected tosubstrate terminal 78 and which have a positive voltage in body region24 will be refreshed with a “1” data state, while those memory cells 50that are commonly connected to the substrate terminal 78 and which donot have a positive voltage in body region 24 will remain in blockingmode, since their SCR device will not be turned on, and therefore memorystate “0” will be maintained in those cells. In this way, all memorycells 50 commonly connected to the substrate terminal will bemaintained/refreshed to accurately hold their data states. This processoccurs automatically, upon application of voltage to the substrateterminal 78, in a parallel, non-algorithmic, efficient process. In oneparticular non-limiting embodiment, a voltage of about 0.0 volts isapplied to terminal 74, a voltage of about −1.0 volts is applied toterminal 70, and about +0.8 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships therebetween. Alternatively, the voltages applied toterminals 72 and 74 may be reversed.

FIGS. 6-8 show another embodiment of memory cell 50 according to thepresent invention. In this embodiment, cell 50 has a fin structure 52fabricated on substrate 12, so as to extend from the surface of thesubstrate to form a three-dimensional structure, with fin 52 extendingsubstantially perpendicularly to, and above the top surface of thesubstrate 12. Fin structure 52 is conductive and is built on buried welllayer 22. Region 22 is also formed by an ion implantation process on thematerial of substrate 12. Buried well layer 22 insulates the floatingsubstrate region 24, which has a first conductivity type, from the bulksubstrate 12. Fin structure 52 includes first and second regions 16, 18having a second conductivity type. Thus, the floating body region 24 isbounded by the top surface of the fin 52, the first and second regions16, 18 the buried well layer 22, and insulating layers 26 (seeinsulating layers 26 in FIG. 8). Insulating layers 26 insulate cell 50from neighboring cells 50 when multiple cells 50 are joined to make amemory device. Fin 52 is typically made of silicon, but may comprisegermanium, silicon germanium, gallium arsenide, carbon nanotubes, orother semiconductor materials known in the art.

Device 50 further includes gates 60 on two opposite sides of thefloating substrate region 24 as shown in FIG. 6. Alternatively, gates 60can enclose three sides of the floating substrate region 24 as shown inFIG. 7. Gates 60 are insulated from floating body 24 by insulatinglayers 62. Gates 60 are positioned between the first and second regions16, 18, adjacent to the floating body 24.

Device 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, bit line (BL) terminal 74, buried well (BW)terminal 76 and substrate terminal 78. Terminal 70 is connected to thegate 60. Terminal 72 is connected to first region 16 and terminal 74 isconnected to second region 18. Alternatively, terminal 72 can beconnected to second region 18 and terminal 74 can be connected to firstregion 16. Terminal 76 is connected to buried layer 22 and terminal 78is connected to substrate 12. FIG. 8 illustrates the top view of thememory cell 50 shown in FIG. 6.

FIG. 9 shows an example of array architecture 80 of a plurality ofmemory cells 50 arranged in a plurality of rows and columns according toan embodiment of the present invention. The memory cells 50 areconnected such that within each row, all of the gates 60 are connectedby a common word line terminal 70. The first regions 16 within the samerow are also connected by a common source line 72. Within each column,the second regions 18 are connected to a common bit line terminal 74.Within each row, all of the buried layers 22 are connected by a commonburied word terminal 76. Likewise, within each row, all of thesubstrates 12 are connected by a common substrate terminal 78.

In one embodiment, the buried layer 76 or the substrate 78 can besegmented (e.g., see FIG. 10) to allow independent control of theapplied bias on the selected portion of the memory array. For example,the buried layer terminals 76 a and 76 b are connected together to forma segment independent of the segment defined by common buried layerterminals 76 m and 76 n in FIG. 10. Similarly, the substrate terminals78 a and 78 b can form a segment that can be biased independently fromother segments, for example, the segment defined by substrate terminals78 m and 78 n. This array segmentation allows one segment of the memoryarray 80 to perform one operation (e.g., read), while the other segmentsperform another operation (e.g., holding).

From the foregoing it can be seen that with the present invention, asemiconductor memory with electrically floating body is achieved, andthat this memory can be operated to perform non-algorithmic refreshmentof the data stored in such memory. Additionally, such restore operationscan be performed on the memory cells automatically, in parallel. Thepresent invention also provides the capability of maintaining memorystates without the need for periodic refresh operations by applicationof a constant positive bias to the substrate terminal. As a result,memory operations can be performed in an uninterrupted manner. While theforegoing written description of the invention enables one of ordinaryskill to make and use what is considered presently to be the best modethereof, those of ordinary skill will understand and appreciate theexistence of variations, combinations, and equivalents of the specificembodiment, method, and examples herein. The invention should thereforenot be limited by the above described embodiment, method, and examples,but by all embodiments and methods within the scope and spirit of theinvention as claimed.

That which is claimed is:
 1. A semiconductor memory cell comprising: atransistor comprising a source region, a first floating body region, adrain region, and a gate; and a silicon controlled rectifier devicehaving a cathode region, a second floating body region, a buried layerregion, and an anode region, wherein: a state of said memory cell isstored in said first floating body region, said first floating bodyregion and said second floating body region are common, said siliconcontrolled rectifier device maintains a state of said memory cell, andsaid transistor is usable to access said memory cell.
 2. Thesemiconductor memory cell of claim 1, wherein: said first floating bodyregion has a first conductivity type selected from a p-type conductivitytype and an n-type conductivity type, said cathode region has a secondconductivity type selected from said p-type and n-type conductivitytypes, said second conductivity type being different from said firstconductivity type, said buried layer region has said second conductivitytype; and said anode region has said first conductivity type.
 3. Thesemiconductor memory cell of claim 1, wherein said silicon controlledrectifier device maintains a state of said memory cell through a biasapplied to said anode region.
 4. The semiconductor memory cell of claim3, wherein said bias applied to said anode region is a constant positivevoltage bias.
 5. The semiconductor memory cell of claim 3, wherein saidbias applied to said anode region is a periodic pulse of positivevoltage.
 6. The semiconductor memory cell of claim 3, wherein said biasapplied to said anode region results in at least two stable states. 7.The semiconductor memory cell of claim 1, wherein said transistor isformed in a fin structure.
 8. A semiconductor memory array comprising: aplurality of semiconductor memory cells arranged in a matrix of rows andcolumns, wherein each said semiconductor memory cell includes: atransistor comprising a source region, a first floating body region, adrain region, and a gate; and a silicon controlled rectifier devicehaving a cathode region, a second floating body region, a buried layerregion, and an anode region, wherein: a state of said memory cell isstored in said first floating body region, said first floating bodyregion and said second floating body region are common, said siliconcontrolled rectifier device maintains a state of said memory cell, saidtransistor is usable to access said memory cell, and wherein said anoderegion is commonly connected to at least two of said memory cells. 9.The semiconductor memory array of claim 8, wherein: said first floatingbody region has a first conductivity type selected from a p-typeconductivity type and an n-type conductivity type, said cathode regionhas a second conductivity type selected from said p-type and n-typeconductivity types, said second conductivity type being different fromsaid first conductivity type, said buried layer region has said secondconductivity type; and said anode region has said first conductivitytype.
 10. The semiconductor memory array of claim 8, wherein saidsilicon controlled rectifier device maintains a state of said memorycell through a bias applied to said anode region.
 11. The semiconductormemory array of claim 10, wherein said bias applied to said anode regionis a constant positive voltage bias.
 12. The semiconductor memory arrayof claim 10, wherein said bias applied to said anode region is aperiodic pulse of positive voltage.
 13. The semiconductor memory arrayof claim 10, wherein said bias applied to said anode region results inat least two stable states.
 14. The semiconductor memory array of claim9, wherein said transistor is formed in a fin structure.
 15. Anintegrated circuit comprising: an array of semiconductor memory cellsformed in a semiconductor substrate having at least one surface, thearray comprising: said semiconductor memory cells arranged in a matrixof rows and columns, wherein each said semiconductor memory cellincludes: a transistor comprising a source region, a first floating bodyregion, a drain region, and a gate, and a silicon controlled rectifierdevice having a cathode region, a second floating body region, a buriedlayer region, and an anode region, a first control circuit configured toprovide electrical signals to said anode region, and a second controlcircuit configured to provide electrical signals to said transistor toaccess said memory cell; wherein: a state of said memory cell is storedin said first floating body region, said first floating body region andsaid second floating body region are common, said silicon controlledrectifier device maintains a state of said memory cell, said transistoris usable to access said memory cell, and wherein said anode region iscommonly connected to at least two of said memory cells.
 16. Theintegrated circuit of claim 15, wherein said first control circuitprovides electrical signals to said anode region to maintain the stateof said memory cells connected to said anode region.
 17. The integratedcircuit of claim 16, wherein said electrical signals to said anoderegion are constant voltage biases.
 18. The integrated circuit of claim16, wherein said electrical signals to said anode region are periodicpulses of voltage.
 19. The integrated of claim 16, wherein saidelectrical signals to said anode region result in at least two stablestates.
 20. The integrated circuit of claim 15, wherein said transistoris formed in a fin structure.